sigmon: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/sigmon - from package: comgt

You may install the required package with command apt-get install {package}

Error in other languages:
sigmon: bevel nie gevind nie
sigmon: comandă negăsită
sigmon: comando não encontrado
sigmon: commande introuvable
sigmon: command not found
sigmon: käsku ei ole
sigmon: không tìm thấy lệnh
sigmon: komanda nerasta
sigmon: Kommando nicht gefunden.
sigmon: kommandot finns inte
sigmon: komut yok
sigmon: nie znaleziono polecenia
sigmon: níor aimsíodh an t-ordú
sigmon: no se encontró la orden
sigmon: no s'ha trobat l'ordre
sigmon: opdracht niet gevonden
sigmon: parancs nem található
sigmon: perintah tidak ditemukan
sigmon: príkaz nenájdený
sigmon: příkaz nenalezen
sigmon: команда не найдена
sigmon: командата не е открита
sigmon: 命令找不到
sigmon: コマンドが見つかりません